Turbo-compressors are widely used for imparting high pressures to gases for a variety of process applications typical of which is for booster transmission of natural gas. Characteristic of such compressors is the need of seals for effective control of gas leakage. In recent years the use of the gas seal has been proposed as a substitute for an oil seal and is generally comprised of a stationary carbon ring axially contiguous to the end face of a high velocity rotor. Formations on the rotor end face in opposition to a balance spring bias, aerodynamically force a laterally controlled separation therebetween through which limited high pressure gas leakage can occur. Gas seals are commercially available from companies such as Crane Packing Company or the Koppers Company.
Required to permit lateral movement of the gas seal is a secondary seal along its inward sliding surface to contain flow against the pressure differential to which the gas seal is exposed. Most often the secondary seal is of the resilient O-ring variety which unavoidably in response to the imposed pressure differential tends to incur a drag force opposing sliding movement contemplated for the gas seal. Since the value of the drag force increases in correlation with an increase in differential pressure across the O-ring, it has been necessary to limit applications of the gas seal to encountered pressure differentials within tolerable levels below which significant binding of the sliding action does not occur. This constraint therefore has resulted in limiting the high side pressure of the apparatus which per se has restricted the applications for which the gas seal can be utilized. While recognizing the handicap imposed by the limits of differential pressure, a ready solution for enabling the use of higher pressure differentials has not heretofore been known.